Control devices of the type mentioned at the outset are generally known. In this context, control functions and control algorithms are used which produce manipulated variables for the driving motors from a speed of the hybrid drive and a torque demand, for example. In the case of an open-loop/closed-loop control of the speed of the hybrid drive, the control device must apportion the torque demand between the electric motor and the combustion engine. If the driving motors are controlled in parallel, a torque reserve must remain for each of them to allow a rapid torque build-up and a fast reaction to load changes in response to a torque demand. The torque reserve of the combustion engine is set in the idle condition of an Otto engine, for example, which is operated at lambda=1 (homogeneous operation), by increasing the air supply in conjunction with a retarding of the ignition timing. This type of combustion-engine torque reserve that is rapidly retrievable in response to advancing of the ignition timing at an operating point having a characteristic speed can be utilized for speed control, but is associated with an increased fuel consumption and increased exhaust emissions.